1. Field of the Invention
The present invention relates to component-embedded substrates in which an electronic component is embedded in a multilayer substrate and manufacturing methods thereof.
2. Description of Related Art
One of examples of conventional component-embedded substrates is disclosed in, for example, Japanese Patent Laid-Open Publication No. 2008-141007. This component-embedded substrate includes an insulating base 601, at least one electronic component 602, a plurality of external electrodes 603, a plurality of wiring conductors 604, and a plurality of interlayer connectors 605 as shown in FIG. 7.
The insulating base 601 may be formed by stacking up a plurality of resin layers 606 (e.g., five resin layers 606a to 606e) in a predetermined direction Z and then adhering the layers together. The resin layers 606a to 606e may be made of a thermoplastic resin. More specifically, the resin layer 606b may be adhered to one of the principal surfaces of the lowermost resin layer 606a, and the resin layer 606c may be adhered to one of the principal surfaces of the resin layer 606b. Likewise, the resin layers 606d, 606e may be adhered to one of the principal surfaces of the resin layers 606c, 606d, respectively.
The electronic component 602 may be buried in a cavity formed inside the above-described insulating base 601. To electrically couple the electronic component 602 with the external electrodes 603, the wiring conductors 604 may be formed on the principal surface of a required resin layer 606. To electrically couple together two wiring conductors 604 formed on resin layers 606 which are adjacent to each other in the layer stacking direction, an interlayer connector 605 may be formed in a resin layer 606 lying between the wiring conductors 604.
The above-described component-embedded substrate may be manufactured generally through the processes which will be described below.
First, a metal foil (e.g., copper foil) may be adhered to one of the principal surfaces of each of the resin layers 606a to 606e that are made of a thermoplastic resin. Thereafter, photolithography and etching may be carried out on this metal foil, whereby the external electrodes 603 and the wiring conductors 604 may be formed as shown in FIG. 8A.
Then, a through hole 607, which is to form the cavity, may be formed in the resin layer 606c. 
Then, via holes 608, which are closed by the wiring conductors 604, may be formed at predetermined positions in the resin layers 606a to 606e. These via holes 608 may be filled with an electrically-conductive paste which is to form the interlayer connectors 605.
After the above-described process, the resin layers 606a to 606e may be stacked up as shown in FIG. 8A. In that process, the electronic component 602 may be placed at a predetermined position on the resin layer 606b and inserted into the through hole 607 of the resin layer 606c. The resin layer 606d may be placed on this resin layer 606c (layer stacking process).
Thereafter, as shown in FIG. 8B, the multilayer body of the resin layers 606a to 606e may be placed between a pair of heat press plates 609a, 609b. The heat press plates 609a, 609b apply pressure and heat to the multilayer body at both surfaces thereof. As a result, the resin layers 606a to 606e may be softened, and adjacent ones of the resin layers 606 may be adhered to each other. In this way, the insulating base 601 may be formed (heating and compression process).
In the heating and compression process, the softened resin layers 606a to 606e may flow, and as a result, the electronic component 602 may be encapsulated in the insulating base 601. At the same time, electrodes 610 of the electronic component 602 may be joined to the wiring conductors 604 or interlayer connectors 605 formed on or in the resin layer 606b. Further, the electrically-conductive paste may be sintered and changed into an alloy, whereby the interlayer connectors 605 electrically coupling the wiring conductors 604 to each other are formed.